1. Field of the Invention
The present invention relates to an optical network terminal for receiving a time division multiple access-passive optical network (TDMA-PON) service using an orthogonal frequency division multiple access (OFDMA)-PON technology, and more particularly, to a structure and a method of a converged PON (CPON) for dynamically providing an upstream transmission bandwidth through allocation of multiple subcarriers to each single optical network unit (ONU).
2. Description of the Related Art
Conventional flow-based Digital Subscriber Line (xDSL) and cable network technologies are unable to support high-quality Internet Protocol Television (IPTV) services and novel subscriber multimedia services requiring a wide transmission bandwidth, efficiently. In order to overcome such a drawback, Fiber To The Home (FTTH) technologies based on a fiber optic cable have been employed as access network technology. As a representative technology applied to the FTTH, a passive optical network (PON) includes an optical line terminal (OLT) installed at a service provider, an optical network unit/terminal (ONT/ONU) installed at a subscriber, and an optical distribution network (ODN) connecting the terminals.
The ODN used in the PON includes only a fiber optic cable and an unpowered passive element and thus, does not involve obstacles created by active elements. Moreover, a long-distance transmission function provided by the fiber optic cable further allows for a telephone company and a subscriber to be separated by a greater distance and thus, contributes to a decrease in the number of telephone companies. Accordingly, since the PON technology enables communications service providers to employ substantially fewer networks and telephone companies, maintenance costs are reduced considerably.
In a general network structure of the PON, an OLT is installed at a local telephone company or a service provider point-of-presence (POP) and a passive element having a 1-to-N distribution is disposed at a location on which subscribers converge, thereby connecting ONUs. Such PON technology is generally classified into a time division multiple access (TDMA)-PON enabling ONUs to transmit data to an OLT via time division multiplexing and a wavelength division multiplexing (WDM)-PON enabling transmission of data by allocating a unique wavelength to each ONU. Currently, only TDMA-PON technology is a standard recommendation and is divided, based on a transmission protocol, into gigabit-capable PON (GPON) of the Telecommunication Standardization Sector of the International Telecommunications Union (ITU-T) Full Service Access Network (FSAN), and an Ethernet PON (EPON) of the Institute of Electrical and Electronics Engineers (IEEE) 802.3.
The IEEE 802.3 completed the 1 Gbps-EPON standard in 2004 and then the 10 Gbps-EPON standard in 2009. The ITU-T (FSAN) completed the asymmetric 2.5 Gbps-GPON in 2005 and then the 10 Gbps-XG-PON1 standard in 2010. In addition, white papers on the NG-PON2 standard including strategies for evolution of future access networks were written, which mention not only next-generation high-capacity TDMA-PONs but also WDM-PON and OFDMA-PON standards. Currently, an EPON and a GPON that belong to TDMA-PON technology are generally applied to access networks. Further, in recent years, to extend transmission bandwidths of the EPON and the GPON, application of a 10 Gbps EPON and an XG-PON1 are being prepared while an existing installed ODN is still in use.
Recently, an OFDMA-PON is receiving attention in light of the ability to extend a transmission bandwidth through multiple subcarriers while adopting an ODN conventionally used in a TDMA-PON without structural change. That is, the OFDMA-PON may provide a broadband access through a combination of the multiple subcarriers and time division in the subcarriers and offer various TDMA-PON services by the subcarriers through the existing ODN.
However, in order to provide existing TDMA-PON services efficiently, through use of the OFDMA-PON, operating a plurality of subcarriers by individual services is recommended, in lieu of allocating a fixed subcarrier to each service. Further, a structure of receiving TDMA-PON services and having a predetermined delay time in an OFDMA-PON section is necessary.